A device including a measuring channel is referred to in German Published Patent Application No. 197 35 891, which houses a measuring element around which the medium entering flows. The measuring channel is slanted at a selected angle in relation to a lengthwise axis of the line, so that the inlet channel includes a region shadowed from a main flow direction. The measuring element is positioned in the shadowed region of the measuring channel in order to avoid fouling and resulting defects of the measuring element.
As a consequence of water entering the intake line, e.g., due to a roadway wet with rain, or the entry of particles, contamination of the measuring element may occur. Natural dissolved salt components contained in this splashed water then produce drift of the characteristic of the measuring element as a consequence of the formation of salt encrustations on the membrane of the sensor part. The particles may damage or even destroy the measuring element. A protected region is formed by the slant of the measuring body, but liquids or particles reach the measuring channel regardless.
A hot-wire airflow meter, referred to in German Published Patent Application No. 197 38 337 and U.S. Pat. No. 5,892,146, includes a bulge upstream from the measuring element which is configured in one piece with a wall of the line. This bulge is not configured in a measuring channel and is not used to deflect liquids or particles.
A measuring device is referred to in German Published Patent Application No. 198 15 654, in which a measuring channel includes a bulge which protects the measuring element from particles. However, this bulge is not used to deflect liquids or particles, so that they may continue to arrive in the channel.
A device is referred to in German Published Patent Application No. 197 35 664 and GB Patent No. 232 85 14, in which the measuring element is positioned inside a tubular body which the medium flows through, an upstream end of the tubular body extending into a filter chamber and including inlet openings on a lateral surface there, in order to reduce the impingement of dirt particles or water droplets on the measuring element. Particularly in the event of very polluted air and a high proportion of water in the intake air of the internal combustion engine, there is the danger of the air filter being soaked with water, which then penetrates through the filter mat and carries along dirt particles at the same time. On the downstream side of the air filter, the actual clean side, the danger arises as a consequence that the intake air again pulls along dirt particles and water droplets from the filter surface, which are then deposited in an undesired manner on the measuring element and result in erroneous measurements or failure of the measuring element. The tubular body of other prior systems reduces the danger of deposits on the measuring element through the arrangement of inlet openings on the lateral surface, however, a correspondingly long configuration of the tubular body causes an undesired pressure drop, which results in reduction of measuring sensitivity. In addition, the reduction of impingement of the measuring element with liquid/solid particles may hardly be ensured at a very high liquid intake of approximately 20 liters/hour.
During the operation of the device, it may occur that, for example, oil droplets or oil vapor are carried along in the air against the main flow direction and the measuring element is contaminated, which significantly worsens the measuring properties. Reasons for the backflow of liquids are, for example, pulsating flows or running on of a turbo charger in the shutdown phase. The inner surface of a protective grid, which is configured including a special wide mesh, is not sufficient as a condensation surface for the liquid.